Stone mill is a kind of machinery to process rice, wheat, beans and other grains into powder or pulp in ancient China. In the days when there were no stone mills,ancient people who wanted to eat rice flour, wheat flour, or bean flour, put the rice, wheat, and beans in stone mortars and pounded them with stone sticks. This method was time-consuming and labor-intensive, and it was only after the invention of the stone mill that grain processing became convenient.

The stone mill was originally called a mill.

Two flat, cylindrical stones of a certain thickness were placed on top of each other to make a mill. The upper one is called the upper fan, which has an eye, called the "grinding eye", and the lower one is called the lower fan, which is fixed on a wooden frame with a shaft in the center, on which the upper fan is set.

Turning the upper fan around the shaft, the stone mill began to work. The space between the upper fan and the lower fan is called the grinding chamber, and the outer circumference of the grinding chamber is the grinding teeth. The grain flows into the mill through the grinding hole, evenly distributed between the upper and lower fans, and as the upper fan rotates, it is ground into a fine powder, which flows from the surrounding crevices onto the grinding disk. People use bamboo sieve to sift the impurities, and then get the finer rice noodles.

The grinding teeth are the core part of the stone mill.

It has gone through three stages of development: early, middle and late. Before the Western Han Dynasty, the grinding teeth of the stone mill were mainly pitted, with rectangular, round and triangular shapes; from the Eastern Han Dynasty to the Three Kingdoms is the second stage, the grinding teeth are radial in shape, and are divided into four, six, and eight zones, dividing the grinding surface into four, six, and eight equal parts on average; the third stage is after the Western Jin Dynasty, which is the mature stage of the development of the stone mill, and the grinding teeth are mainly of the eight-zone diagonal type, and there are also ten-zone diagonal type. Such a mill grinds out a more delicate powder.

Stone mill initially rely on human or animal power to push. By the Jin Dynasty, mills using water power as a motive force appeared.

The water mill consists of a grinding disk made of two round stones, a rotating shaft, a water wheel disk, and a stand. The upper mill is suspended from the stand, the lower mill is mounted on a rotating shaft, and the other end of the shaft is equipped with a water wheel disk, which is flushed by the potential energy of water, thus driving the rotation of the lower mill.

According to the impulse power of running water, the ancients invented two kinds of water mill. Where the impulse of water is relatively large, the power part of the water mill is a horizontal water wheel, the vertical axis of the wheel to install the upper fan of the mill, to the impulse of running water water wheel, to drive the mill to rotate.

If the water impulse is relatively small, but the water is relatively large, people install another form of water mill: power part of a vertical wheel, in the wheel shaft installed on the wheel of a gear, and the mill shaft of the lower part of the flat-mounted a gear connection. The water wheel turns the mill by the movement of the gear.

Summary:

The use of water mills greatly increased productivity and allowed for the production of fine rice noodles in large quantities. Developed later, a water wheel can drive several mills to rotate, reflecting the principle of hydroelectric power power, this kind of water mill is called the water turn even machine mill . Yuan dynasty agronomist Wang Zhen Nongshu documented in the water turning machine mill, a water wheel can drive nine mills work at the same time, high efficiency.